This invention is directed to a draw-lofting process for man-made yarns and particularly to polyester continuous filament yarns and fabrics including such yarns.
Previous lofted yarn products have been made using fully processed continuous filament yarns which are overfed to a high-pressure air jet device. Those products can be made with a single-end overfeed or with dual-end feed. In the case of polyester yarn, for instance, drafting may have been accomplished either on a draw-twister or on a continuous spin draw type apparatus.
U.S. Pat. No. 2,852,906 to Breen, for example, is representative of the prior art by which a bulky continuous filament yarn is achieved by passing a bundle of continuous filaments through a high velocity air jet in which the individual filaments are caused to become separated and whipped about sufficiently to form coils, loops or whorls at random intervals along their lengths. The various irregularly spaced convolutions in the yarn provide a lateral interfilament spacing important in producing the bulk and resulting garment warmth of fabrics made from such yarn.
As explained in an earlier Breen, U.S. Pat. No. 2,783,609, the "loops" indicated refers to tiny complete loops formed by a filament doubling back upon itself, crossing itself and then proceeding in substantially the original direction. In mathematics, a curve of this type is said to have a crunode; thus the term "crunodal loops" was derived by the patentee to distinguish in his specification those loops from other forms of loops. The patentee explained that the majority of loops visible on the surface of the yarn of his invention were of a roughly circular or ring-like shape. The crunodal loops inside of the yarn were not readily studied but that it was evident that the pressure of surrounding filaments would tend to cause such loops to assume more complex shapes. Breen reported that the most obvious characteristics of his continuous filament yarn were its bulkiness and the presence of a multitude of filament ring-like loops irregularly spaced along its surface.
The Breen patents explain that a stream of air or other compressible fluid is jetted rapidly from a confined space to form a turbulent region in which yarn passing therethrough is supported by the fluid stream and the individual filaments are separated from each other and whipped about violently in the turbulent region. As the separated filaments are removed from the turbulent region, they are swirled into convolutions which may be held in place by adjacent filaments of the reforming yarn bundle. The resulting bulkiness of the yarn may be stabilized by an additional treatment such as by twisting the filaments together, thereby increasing the friction between filaments to hold the convolutions more firmly in place. The yarn may then be wound up for subsequent processing.
As shown by the numerous examples in the Breen patents, and as explained on page 549 in the text, "Man-Made Fibers" (4th Edition -1963) by R. W. Moncrieff, Publisher: Heywood & Company Limited in London, England, the yarn is fed through an air jet to take-up rollers which draw off the yarn at a speed lower than the speed at which it is fed to the jet. Since the take-up speed is slower than the feed speed, the air-jet forms numerous randomly spaced loops, thereby taking up the slack in the filaments produced by the overfeed. As also explained in the text, the process does not depend on the thermoplasticity of the fiber and thus can be applied to any continuous multi-filament yarn, such as viscose rayon. The Breen patents also give as examples nylon (polyhexamethylene adipamide), glass, polyethylene terephthalate, cellulose acetate, acrylic and vinyl chloride-acrylonitrile copolymer yarns.
In still another Breen U.S. Pat. No. 2,869,967, it is pointed out that the amount of "overfeed," which characterizes the difference between yarn feed and yarn take-up or wind-up, is one of the factors that controls the amount of bulking action accomplished in the air jet and should generally be in the range of 5% to 50%, depending upon the effect desired.
The above-described operation is to be contrasted with the process disclosed in this invention wherein the yarn is fed to a gaseous jet device at one speed and is taken up from the gaseous jet device at a greater speed due to the drafting operation that occurs within the jet device. The process is not only further distinguished from the prior art in that the gases within the jet device are heated so as to raise the temperature of the yarn above the glass transition temperature and with the induced drag forces cause the drafting of the yarn to occur, but also that the drafting is a nonuniform or differential drafting resulting in the formation at random intervals along each of the filaments of coils, loops or whorls. The coils, loops or whorls in each filament are held in place by similar formations in adjacent filaments when the filaments recombine to form a single yarn bundle upon leaving the gaseous jet device. The yarn bundle has also been stabilized by having been heat set while within the gaseous jet device.